LA-ICP-MS Zircon U–Pb ages of the Ryugamori Granitoids, northern Akita Prefecture, Japan

Abstract

The Ryugamori Granitoids in northern Akita Prefecture, northeast Japan, were emplaced during two separate phases of magmatism. In this study, we determined the ages of the granitoids using LA–ICP–MS zircon U–Pb dating. Ages of 21.9 ± 0.2 Ma and 21.2 ± 0.2 Ma were obtained from the older Ryugamori Granitoids, while the younger granitoids were dated to 9.5 ± 0.1 Ma. A porphyritic granite in the southwestern part of Ryugamori, which was previously thought to be a member of the younger Ryugamori Granitoids, yields an age that corresponds to the older phase of granitoid emplacement. The distribution of the younger Ryugamori Granitoids is limited to the southern part of the Ryugamori area.